Marine propulsion apparatus

ABSTRACT

A propulsion system for a boat is hydraulically driven and has a propeller close-coupled to an immersible hydraulic motor unit, the motor unit being carried on a support enabling the motor unit to swivel, for steerage, and to tilt so that the thrust developed by the propeller can be used to assist in trimming the boat fore and aft, the support furthermore enabling the motor unit and propeller to be swung into an enclosing casing for their protection when out of use.

[ Aug. 26, 1975 United States Patent [191 Scott 3,483,843 12/1969 Hawthornc.u..................... 115/41 R 1 MARINE PROPULSION APPARATUS [76] Inventor:

3,581,702 6/1971 'Moberg......... 3,702,485 11/1972 Thompson.......

Claude Worthington Scott, Throstle Nest Farm, Summerbridge, near Harrogate England Primary Examiner-Trygve M. Blix Aug. 20, 1973 Assistant ExaminerSherman D. Basinger [22] Filed:

Attorney, Agent, or FirmR0bert F. OConnell [21] Appl. No.: 390,120

[52] US. 115/41 R; 115/34 A; 115/35 Int. B631) 5/06 draulic motor unit, the motor unit being carried on a support enabling the motor unit to swivel, for steer- 1 A 1. v/ 59 3. 4 7 34 5O 6 H m5 "6 6 h c r a e S f 0 M .w F m 5 .1.

age, and to tilt so that the thrust developed by the propeller can be used to assist in trimming the boat fore and aft,

[56] References Cited UNITED STATES PATENTS the support furthermore enabling the motor 2,984,985 60/471 unit and propeller to be swung into an enclosing as- 3,139,062 6/1964 115/34 A ing for their protection when out of 3,240,452 3/1966 Cheeseboro 115/41 HT 3 306 246 2/1967 Rcdcr 114/66 5 H 12 Claims, 4 Drawing Figures PATENTEU wezsms SHEET 1 [If 3 MARINE PROPULSION APPARATUS The present invention relates to improvements in marine propulsion apparatus suitable, inter alia, for small craft including sailing yachts.

According to the present invention, there is provided marine propulsion apparatus including a casing, for fitting to the hull of a boat, and propulsion unit which includes an underwater-thrust-generating means, the casing including an opening and mounting means bearing the thrust generating means, and the mounting means enabling the thrust generating means to be moved through the opening between parked and operative positions, the thrust generating means being contained substantially wholly within the casing in its parked position and being located outside the casing in its operative position.

Preferably, the thrust generating means is a hydraulic motor which is coupled to a propeller or impeller through a drive shaft, the motor being contained within a sealed housing. The apparatus forms part of a propulsion system including a hydraulic pump and an engine for driving the pump, the engine being an internal combustion engine, although conceivably other motors such as electric motors could be used. The apparatus is primarily intended for propelling small craft, although it could be used in larger vessels, particularly as an aid to manoeuvring. Thus, the apparatus can be located at bow and stern of a vessel for pushing the vessel sideways towards or away from a quayside. The hydraulic pump can be of a similar or identical design to the hydraulic motor, which is preferably a piston-type motor.

The mounting means could incorporate telescopic means for moving the unit. Preferably, however, the mounting means is of a pivotal nature enabling the underwater unit to be swung about the pivot axis of the mounting means for movement between the parking and operative positions.

Preferably, the unit is rotatably carried on the mounting means such that, in use, thrust developed by the propeller or impeller can be directed for steering purposes. If it is arranged that the underwater unit is rotatable through 360 about the rotary steering axis, then the thrust developed by the propeller or impeller can be used for braking or reverse propulsion. Best results are attained if the apparatus is installed such that the steering axis is substantially vertical.

It may be more desirable, however, if braking and reverse propulsion are achieved by reversing the motor rather than through the steering equipment. With hydraulic motors, reverse drive can quite easily be attained by reversing the direction of fluid flow through therethrough, using appropriate change-over valves.

The hydraulic motor can, in fact, consist of two or more individual motors coupled to the same drive shaft. In this way, the overall diameter (and hence frontal area) of the housing can be minimised without sacrificing power. Where two or more motors are employed, one can be reversible while the remainder are unidirectional. Then fast forward drive is attainable with all motors operating and slow reverse with just the reversible motor operating, the remainder free wheeling.

Advantageously, the unit is tiltably secured to the mounting means to allow the direction of thrust developed, in use, by the propeller or impeller to be adjusted relative to the waterline. This adjustment makes it possible for the direction of thrust to be set for optimum performance taking into account the balance, loading and normal boat speed. Means for effecting tilting may be such that the trim is adjusted only rarely, although it is preferred that the tilting means are adjustable at any time. The adjustable tilting means can include hydraulic rams or jacks controllable by the helmsman, whereby he can trim the boat whenever warranted by changes in load, speed, wind or sea conditions.

It is preferred that the apparatus is mounted with the steering axis substantially vertical, the pivot axis of the mounting means extending in the fore-and-aft direction, and the tilting axis extending athwartships.

The invention-will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a side elevational view, with parts in section, of propulsion apparatus embodying the invention,

FIG. 2 is a front elevational view, with parts in section, of the apparatus shown in FIG. 1,

FIG. 3 is a block diagram showing a complete hydraulic installation embodying the invention, and

FIG. 4 is another block diagram showing an alternative hydraulic installation.

The propulsion apparatus is shown in FIGS. 1 and 2 of the drawings installed in a boat, the hull of which is indicated at 10. The apparatus 11 includes a casing 12 and an underwater-propulsion unit 13. The unit 13 includes a housing 14 which is of a streamlined bulbous form, the housing forming a sealed container for a hydraulic motor 15 shown in FIGS. 3 and 4. The motor 15 drives a conventional propeller 16 through a drive shaft 18. The motor 15 is a piston-type hydraulic motor, although a gear or vane type motor could be substituted, and is fed with pressurised operating fluid via supply and return ducts, not shown. The ducts lead to a pump 20 driven by an internal combustion engine 21, the pump 20 and engine 21 being at any convenient location within the boat. At least these portions of the ducts within the casing 12 are flexible, pressure piping, and indeed it may be preferred that the complete run of duct from pump 20 to motor 15 is flexible, for safety and to facilitate installation. The motor 15 and pump 20 are of similar construction.

The unit 13 is constructed such that the motor housing 14 and propeller 16 can be moved into and out of the casing 12. The motor housing and propeller are contained wholly within the casing 12 when the propulsion apparatus is idle, and are lowered through an opening 22 to an operative position in which they project outwardly from the hull 10, as illustrated in FIGS. 1 and 2. The opening 22 is aligned with a corresponding opening in the hull 10, and the casing 12 is secured to the hull 10 in a watertight manner.

Retraction and lowering of the motor housing 14 and propeller 16 is achieved in this instance by a sideways swinging movement. The housing 14 is secured to one end of a support member 24 which projects radially from a rotatably-mounted shaft 25 extending across the casing 12. At one end, the shaft 25 is joumalled on a bearing 26 fast with the inside surface of one wall of the casing 12. At its other end, the shaft has a stub spindle 27 which projects through an intermediate wall 28 of the casing 12 into a compartment 29 thereof. The stub spindle is borne in a bearing 32 fast with the wall 28 and is attached to lifting means 33 to be described. A flexible rubber boot 34 provides a seal preventing water entering the compartment 29. Since,,in use, the part of the casing 12 which receives the housing 14 and propeller 16 is always flooded, the bearing 26, at least, can be nylon.

The illustrated apparatus is intended to provide steerage as well as propulsion, and for this purpose the motor housing 14 and propeller 16 are rotatably mounted. It is desirable that the rotation be about a substantially vertical axis when the housing 14 is in the lowered, operative position. Inwardly of the opening 22 the support member 24 has a hollow cylindrical portion 36 through which the ducts to the motor are threaded. The portion 36 is rotatably received inside a sleeve 37. The sleeve 37 passes through the shaft 25 transversely and is welded thereto. The cylindrical portion 36 is joumalled on bearings 38, for example of nylon, and is retained in position by a cap 40 on its inner end. The support member 24 is provided with a drum portion 41 which is grooved to receive a steering cable, not shown. The cable is led out of the casing 12 through appropriate seals to a steering wheel within the boat. Some simplification of the steering cable arrangement can be achieved if the drum 41 is attached to or integral with the cap 40. The drum 41 would then swing through a relatively small distance whenever the lifting means is operated. An advantage of this construction is that the housing 14 and propeller 16 can be turned through 360. Taking their position shown in FIG. 1 as corresponding to normal straight ahead driving, it will be realised that thrust reversal for'braking and reverse drive are gained merely by causing the propeller 16 to face in the opposite direction. The support member 14 couldbe fitted with a steering yoke instead of the grooved drum portion, but then thrust reversal as just described could not be attained. Y

The apparatus is also-provided with means for adjusting thethrust angle, that is the angle between the direction of thrust and the waterline. The construction of the adjusting means could be such as to permit the making of semi-permanent adjustments which are carried out upon installation and periodically thereafter. This would be satisfactory if the apparatus is intended for use in a sailing boat. For use in high performance power boats, however, it is preferred that the adjustment means is readily and continuously adjustable under way by the helmsman. Such a construction is shown in FIGS. 1 and 2.

The support member 24 is bifurcated and the housing 14 is pivotally mounted between its two legs. At the top of the housing 14 is an apertured lug 42 to which the piston arm 43 of a double-acting hydraulic jack 44 is attached, the jack 44 being secured within the hollow cylindrical portion 36. As will be appreciated, extension and contraction of the jack 44 tilts the propeller 16 upwardly and downwardly, respectively. The jack 44 is connected through a suitable control valve either to the pump or to a subsidiary pump, also driven by the engine 21, which may be provided, for separate lubrication of the motor bearings and for establishing a small positive pressure within the housing 14 to provide an oil seal therefor. With this adjustment means, the helmsman can readily trim the boat to Suit the load carried, speed and sea conditions.

It can be arranged for the jack 44 to maintain the housing 14 in a selected tilt attitude, but this would require a continuous oil pressure in the jack. The existence of -a continuous oil pressure would require efficient and relatively expensive seals, which are resistant to sea water, to prevent leakage. Accordingly, it is preferred to apply oil pressure to the jack only when it is desired to change the tilt attitude of the housing. A holding mechanism, not shown, is therefore provided to lock the housing in set tilt attitudes.

The holding mechanism can consist of a springloaded detent and ratchet, the detent for example being a reciprocatable plunger carried by the support member 24 which is biased to engage a notched member fast with the housing 14.

The vulnerable part of the jack, namely the point at which the piston rod enters the body of the jack 44 is protected from the effects of sea water by a bellows seal 45.

Other tilt adjustment means which could be used could well incorporate or function additionally as a holding mechanism. The tilting means could, for instance, consist of a screw-jack, a worm-and-pinion, a rackand-pinion, a chain drive, and the like, which can be motor driven or manually driven.

The lifting means 33, for rotating the shaft 25 and thereby retracting and lowering the housing 14 and propeller 16, are contained within the compartment 29. The means 33 comprise a double-acting hydraulic jack 50 and a form of toggle or over-centering mechanism 51. The jack 50 is pivotally secured at its end 52 to the casing 12 and its piston rod is likewise pivotally connected to a crank arm 53 of the mechanism 51. The arm 53 is fast with the stub spindle 27. The mechanism 51 is completed by a tension spring 54 secured between the free end of arm 53 and a point 54 below the shaft 25. Movement of the arm 53, is limited to the dashed area shown in FIG. 2 by stops 55, which thereby limit the rotation permitted to the shaft 25. The effect of the spring 54 is to hold the arm 53 in one or the other of its extreme, limit positions, and thus to secure the housing 14 and propeller 16 in either of their retracted or lowered, operative positions. As with the jack 44, the jack 50 is connected through suitable ducts either to the pump 20 or to the said subsidiary pump.

Whilst the over-centering toggle linkage 51 is preferred, other linkages can be devised, but means should be provided to lock the housing 14 and propeller 16 in their raised and lowered positions. Operating means other than a hydraulic jack could be used, although a jack is preferred. With a jack, the provision of separate means for holding the underwater unit in the lowered position could be rendered unnecessary. Then, the pressurised fluid could be delivered to the jack continuously whilst the engine is operating to ensure that the jack holds the underwater unit down. It is better to include separate means for locking the underwater unit down, however, to avoid potential difficulties in sealing the jack against leakage of the continuously applied pressurised fluid.

The casing 12 is completed by doors which are shaped to conform to the adjacent area of the hull 10. One door is fast with the support member 24 and shaft 25 so as to rotate therewith, and is only used when the housing 14 and propeller 16 are parked within the casing 12. The other door 61 is hinged to the casing 12 and its movements are controlled by a mechanism comprising another jack 63 and toggle linkage 64. It is arranged that the jack 63 operates in timed relationship with the main lifting jack 50 whereby the door 61 is moved in synchronism with the movement of the housing 14 and propeller 16. The, jack and toggle are each pivotally secured to a flange portion of the casing 12, outside the cavity thereof. A flexible sealing boot 65 is thus provided to prevent water entering the boat from the inside the cavity of the casing 12.

As noted above, the door 60 is ineffective in the position of the parts shown in FIGS. 1 and 2. To close the casing 12, a further door is provided, but is not fully to be seen in the drawings. The further door is also fast with the member 24 and shaft 25, and has a skirt portion 66 which embraces the steering drum 41.

It will be appreciated that the doors do not prevent the inside of the cavity flooding, but do reduce drag. This is particularly advantageous where the apparatus is fitted to a sailing boat, when the apparatus is idle and the boat is proceeding under sail. It is also, of course, advantageous in a high-performance power boat, and whenever a boat is left at moorings. The rate of accumulation of weed is reduced and damage to the parked propulsion unit is effectively prevented should the boat settle onto the seabed at low tide and when beaching the boat. It could be arranged that the door 61 is held down when the apparatus is operating, so as to act as a steadying fin.

The apparatus shown in FIGS. 1 and 2 is best installed in a boat in such a way that the longitudinal axis of the shaft 25 is parallel to the fore-and-aft axis of the boat. Desirably the housing 14 tilts about an athwartships direction and rotates about a vertical axis. Departure from this preferred installation is permissible, however. The actual position of the propulsion apparatus is largely a matter of convenience. It is preferred, however, to locate the apparatus some way forward of the stern of the boat. Then, any upthrust developed by the propeller 16 can be deflected by the underside of the hull. In this way, loss of propulsive effort by creating surface turbulence such as exhibited by outboard motors can be avoided. The apparatus may be positioned anywhere along the length of the hull, but is preferred a distance equal to about one third of the overall length of the boat forward of the stern.

The propulsion apparatus shown in FIGS. 1 and 2 forms part of a complete installation including the engine 21 and pump 20. These are positioned at any convenient position within the boat, for example where their bulk, noise and vibration can be most easily accepted. It may be desirable to locate them up forward, where their weight will help to balance a planning type of high performance power boat.

The simple hydraulic circuit shown in FIG. 3 provides for forward and also reverse drive of the motor 15. Reverse driving of the motor may be more convenient than rotating the housing 14 and propeller 16 until they face forward. Two ducts 70, 71 connect the motor to a control valve 72 located in the cockpit of the boat. The valve 72 is a change-over valve for selectively connecting the ducts 70, 71 to either of two further ducts 73, 74. These lead, respectively, to the inlet and outlet of the pump 20. The valve 72 thus permits the flow of pressurised fluid to the motor to be reversed. The control valve 72 also has an intermediate setting wherein the outlet duct 74 can be connected through a by-pass duct 75 either to a reservoir 76 or, as shown, back to the inlet of the pump 20. Conveniently, the valve 72 is operated by an actuator in the form of a handle 77 which selects forward drive when pushed forward and vice versa. The intermediate setting is gained when the handle is likewise in an intermediate position, thereby giving a neutral when the engine 21 is idling. The handle is advantageously linked to an engine throttle 78 such that progressively larger movements of the lever accelerate the engine and thus increase the flow of pressurised fluid delivered by the pump 20.

Although the propulsion apparatus described in detail above hasbut one hydraulic motor, it is to be understood that two or more separate motors driving one and the same drive shaft 18 and propeller 16 could be used insteadThe separate motors could be of smaller size and capacity than a single motor so that the overall diameter and frontal area of the housing 14 can be kept small without unduly sacrificing power. A relatively long housing would then be needed.

A suitable hydraulic circuit is shown in FIG. 4, where the same reference numbers are used for parts which correspond to the like numbered parts of FIG. 3.

One of the separate motors 15a is of a reversible nature and the'others 15b, 150 are of a unidirectional nature. The reversible motor 15a provides both forward and reverse power whilst the remainder only provide forward power. In this way, slow reverse is obtainable from the reversible motor 15a alone (with the remainder free wheeling) and fast forward drive at full power when all three motors are driven.

A somewhat more complex control valve 79 is needed, which incorporates a change-over function for selectively connecting either duct 80 or 81 to the pump outlet duct 74, depending on whether forward or reverse drive is required for the motor 15a. When forward is required, the valve 79 feeds fluid not only to motor 15a but also to the parallelconnected motors 15b, 15c via feed duct 82. The valve 79 is arranged to disconnect the motors 15b, 15c from the pump 20 when reverse drive is selected, the motor 15b, then free-wheeling. The valve 79 also includes a by-pass element for dumping the output of the pump 20 either to the reservoir 76m back to the pump inlet when neutral is required:-

Means for supplying pressurised fluid, and for controlling the fluid, to the jacks 44, 50 and 63 are not shown in FIGS.- 3 and 4 for simplicity. The arrangement can be quite straightforward, and as said earlier, the source of pressurised fluid can either be the main pump 20 or a subsidiary pump, not shown, which delivers lubricating oil to bearings in the motor 15.

It will be appreciated that any one boat may incorporate two or more units as illustrated in FIGS. 1 and 2. Each may be supplied with pressurised hydraulic fluid by separate pumps or by a single pump 20. Moreover, where separate pumps are utilised, each may be individually driven by separate engines or by a single, large engine. A particularly advantageous arrangement is obtained if two underwater propulsion units are employed in the one boat. If the units are located in the region of the bows and stem respectively, are both steerable and are suitably coupled, great manoeuverability can be achieved. It is possible for the boat to be turned about its mid-length point even, allowing it to turn within its own length. Furthermore, such an arrangement allows the boat to be propelled sideways, thus facilitating movement towards and away from a landing stage. The units are desirably located one third or thereabouts of the length of the boat away from its ends.

Suitably hydraulic motors and pumps are commercially available in a range of power ratings, for example from Volvo.

The present invention has numerous advantages, including the ability of mounting the propulsion apparatus 11, the engine and pump in any position in a boat, where they will be most efficient hydronamically and least inconvenient and obstructive. Another advantage lies in the fact that the need for a bulky and heavy propeller shaft associated with a conventional inboard engine is eliminated, as well as the need for a stern gland which frequently proves troublesome. The engine and pump are preferably positioned as low as possible in the boat in order to keep top-hamper to a minimum. Another advantage of the present invention is that geartrains conventionally used in the transmission of existing marine engines are eliminated. Thus noise is kept to a minimum. Furthermore, apparatus embodying the invention is of such a nature that there is no need to align the engine with the propeller assembly unlike conventional marine drive units.

Although a hydraulic motor driving a propeller or impeller has been described in detail, other thrust generating means could be employed. For example, an electric motor could be substituted for the hydraulic motor. Furthermore, the thrust generating means could be of a reaction or jet type, thus avoiding the need for a propeller or impeller. The thrust generating means would then comprise a jet nozzle fed with sea water from a water pump within the boat.

I claim:

1. A marine propulsion apparatus comprising an apertured casing adapted for attachment to the hull of a boat, a propulsion unit, mounting means within said casing mounting the propulsion unit for movement through the aperture of the casing between a parked position within said casing and an operative position below the hull, the propulsion unit comprising a propeller, a drive shaft attached to the propeller, a sealed housing and a hydraulic motor within said housing, said motor being coupled to said propeller through said drive shaft, and said mounting means including a leg carrying said propulsion unit, the leg being mounted on a pivot to swing the propulsion unit laterally of the hull between the operative and parked positions, the drive shaft of the propulsion unit lying generally parallel to the pivot axis of said leg when the propulsion unit is in the parked position.

2. A marine propulsion apparatus as claimed in claim 1 wherein said mounting means includes a coupling between said leg and said pivot permitting rotation of the propulsion unit with said leg about an axis transverse to the propeller drive shaft.

3. A marine propulsion apparatus as claimed in claim 2 wherein said pivot is joumalled in said casing and said coupling comprises a transverse bore in said pivot, one end of said leg being joumalled in the transverse bore for rotation about the said axis.

4. A marine propulsion apparatus as claimed in claim 1 in which the propulsion unit is connected to the said leg by a hinge whose axis is transverse to the propeller drive shaft and means are provided to tilt the propulsion unit about said hinge in order to change the angle of the drive shaft to the water line.

5. The apparatus of claim 4, wherein said tilting means includes a hydraulic jack secured at one end to said leg and at its other end to said propulsion unit.

6. A marine propulsion apparatus as claimed in claim 1 in which the pivot for said leg comprises a shaft journalled in the casing and means are provided for rotating said shaft to effect swinging of the propulsion unit between the operative and parked conditions.

7. The apparatus of claim 6, wherein said shaft rotating means comprises a hydraulic jack and an overcentering device linking said jack and shaft, said overcentering device having an arm fast with said shaft and connected for movement with a piston rod of said jack, and a tension spring being connected to said arm for biasing it in one or other of two extreme positions corresponding to the parked and operative positions of said unit.

8. The apparatus of claim 1, wherein doors are provided to close the aperture of said casing at least when said unit is in its parked position.

9. The apparatus of claim 8, wherein the door movements are controlled by a hydraulic jack and toggle mechanism, and wherein operation thereof is synchronised with movements of said unit between its parked and operative positions.

10. The apparatus of claim 1, wherein said motor includes a plurality of piston-type hydraulic motor units coupled together to said drive shaft, one of said motor units being reversible and the remainder thereof being unidirectional.

11. The apparatus of claim 1, in combination with a hydraulic pump and driving engine therefor, said pump being of the same type as said motor, and flexible piping being used in ducts connecting said motor and said pump.

12. The apparatus of claim 11, further including a control valve for switching the output of said pump between said motor for driving the motor, and a by-pass duct for rendering said motor idle, said valve having an actuator which is linked to said engine for controlling the speed of the latter. 

1. A marine propulsion apparatus comprising an apertured casing adapted for attachment to the hull of a boat, a propulsion unit, mounting means within said casing mounting the propulsion unit for movement through the aperture of the casing between a parked position within saId casing and an operative position below the hull, the propulsion unit comprising a propeller, a drive shaft attached to the propeller, a sealed housing and a hydraulic motor within said housing, said motor being coupled to said propeller through said drive shaft, and said mounting means including a leg carrying said propulsion unit, the leg being mounted on a pivot to swing the propulsion unit laterally of the hull between the operative and parked positions, the drive shaft of the propulsion unit lying generally parallel to the pivot axis of said leg when the propulsion unit is in the parked position.
 2. A marine propulsion apparatus as claimed in claim 1 wherein said mounting means includes a coupling between said leg and said pivot permitting rotation of the propulsion unit with said leg about an axis transverse to the propeller drive shaft.
 3. A marine propulsion apparatus as claimed in claim 2 wherein said pivot is journalled in said casing and said coupling comprises a transverse bore in said pivot, one end of said leg being journalled in the transverse bore for rotation about the said axis.
 4. A marine propulsion apparatus as claimed in claim 1 in which the propulsion unit is connected to the said leg by a hinge whose axis is transverse to the propeller drive shaft and means are provided to tilt the propulsion unit about said hinge in order to change the angle of the drive shaft to the water line.
 5. The apparatus of claim 4, wherein said tilting means includes a hydraulic jack secured at one end to said leg and at its other end to said propulsion unit.
 6. A marine propulsion apparatus as claimed in claim 1 in which the pivot for said leg comprises a shaft journalled in the casing and means are provided for rotating said shaft to effect swinging of the propulsion unit between the operative and parked conditions.
 7. The apparatus of claim 6, wherein said shaft rotating means comprises a hydraulic jack and an overcentering device linking said jack and shaft, said overcentering device having an arm fast with said shaft and connected for movement with a piston rod of said jack, and a tension spring being connected to said arm for biasing it in one or other of two extreme positions corresponding to the parked and operative positions of said unit.
 8. The apparatus of claim 1, wherein doors are provided to close the aperture of said casing at least when said unit is in its parked position.
 9. The apparatus of claim 8, wherein the door movements are controlled by a hydraulic jack and toggle mechanism, and wherein operation thereof is synchronised with movements of said unit between its parked and operative positions.
 10. The apparatus of claim 1, wherein said motor includes a plurality of piston-type hydraulic motor units coupled together to said drive shaft, one of said motor units being reversible and the remainder thereof being unidirectional.
 11. The apparatus of claim 1, in combination with a hydraulic pump and driving engine therefor, said pump being of the same type as said motor, and flexible piping being used in ducts connecting said motor and said pump.
 12. The apparatus of claim 11, further including a control valve for switching the output of said pump between said motor for driving the motor, and a by-pass duct for rendering said motor idle, said valve having an actuator which is linked to said engine for controlling the speed of the latter. 